Astrophysics (Index)About

spectral line

(dark or light line in a spectrum)

A spectral line (or just line) is a dark or light line within a continuous spectrum. For example, a SED representing the spectrum of some object's light may generally be described curve, i.e., nearby wavelengths have nearly the same brightness. A "spike" in the SED indicates wavelength at which light has a much higher magnitude than nearby wavelengths, or a dip, where a wavelength has a much lower magnitude than nearby wavelengths. If the spectrum is displayed as a rectangular area with the source's wavelengths spread across a dimension (per a plate produced a spectrograph), each of these shows as a line, lighter or darker than its surroundings.

In a source's spectrum, light lines are generally caused by emissions at specific wavelengths (emission lines), and dark lines are caused by absorption at specific wavelengths (absorption lines). Lines are related to chemical makeup of the light source or absorber, indicating changes of energy level of electrons, which have characteristic values based upon chemistry. Details of lines can show other characteristics of the light source or intervening absorber such as velocity, turbulence, etc. The term line broadening refers to the mechanisms that create the shape of a line, e.g., in electromagnetic radiation from a star.

Among the widely used spectral lines are the hydrogen series of lines, e.g.,

Atomic spectral lines are sometimes classified by element and ionization, specified by the chemical symbol followed by a Roman numeral, I meaning neutral, II meaning singly ionized positive, III meaning doubly ionized, etc.

Spectral-line mapping refers to imaging or surveying a portion of the sky for the presence of particular spectral lines, often noting their redshift, to determine their radial velocity. Its uses include investigations of accretion disks, jets, molecular clouds, the entire Milky Way, and other galaxies.

Further reading:

Referenced by pages:
absorption line
active galactic nucleus (AGN)
Am star
Australian Square Kilometre Array Pathfinder (ASKAP)
Balmer jump
Balmer series (H)
broad emission line region
broad-line region (BLR)
blue horizontal branch (BHB)
Bohr model
Brackett series
calcium (Ca)
calcium-rich gap transient
carbon (C)
ionized carbon fine structure line ([CII])
carbon monoxide (CO)
cold gas
continuous absorption
continuous spectrum
continuum emission
core collapse supernova (CCSN)
cosmological time dilation
dark matter
velocity dispersion (σ)
Doppler broadening
double-line spectroscopic binary (SB2)
electron orbital
electron shell
emission line galaxy (ELG)
emission line
Faber-Jackson relation (FJR)
falling evaporating body (FEB)
fine structure
forbidden line
full width at half maximum (FWHM)
gravitational redshift
ground state
Gunn-Peterson trough
H-alpha (Ha)
Hydrogen Accretion in Local Galaxies Survey (HALOGAS)
helium 1083 nm line
neutral atomic hydrogen (HI)
HI region (HI)
hydrogen (H)
hydroxyl (OH)
hyperfine structure
ionization correction factor (ICF)
intensity mapping
K correction
Kepler radius
kinematic distance
Kirchhoff's laws
Lyman-alpha emitter (LAE)
L-type star (L)
Lick indices
line blanketing
line broadening
line shape function
Lick Observatory Calcium Line Survey (LkCl)
Lyman alpha (Ly-α)
Lyman-alpha forest
Lyman series (L)
M-type star (M)
metallicity (Z)
Millimeter-wave Intensity Mapping Experiment (mmIME)
molecular cloud
Molecular Deep Field
nitrogen (N)
oxygen lines
PAH emissions
Paschen series
P Cygni profile
planetary nebula luminosity function (PNLF)
position-position-velocity space (PPV)
radial velocity (RV)
radioactive decay
redshift (z)
radial velocity method
Schuster-Schwarzschild model
shell star (sh)
silicon (Si)
spectral line energy distribution (SLED)
supernova (SN)
Sobolev approximation
sodium (Na)
spectral band
spectral class
spectral line designation
spectral signature
spectroscopic binary (SB)
state of excitation
state of ionization
stellar model atmosphere
stellar rotation
stellar temperature determination
S-type star (S)
sulfur (S)
surface abundance
surface gravity
surface temperature
T-type star (T)
telluric star
Tomographic Ionized-carbon Mapping Experiment (TIME)
21-cm line
Type Ia supernova
virial theorem
Voigt profile
water lines
weak-line star
white dwarf (WD)
Wilson-Bappu effect
CO to H2 factor (Xco)
Zeeman-Doppler imaging (ZDI)
Zeeman effect